Latest Updates



Click for seminar details


KOI logo (135)
Who are we?




Trickle tower update02     (Trickle tower update)


I wrote the following articles for Koi Carp Magazine.
Therefore they own the copyright but the Editor has given permission for them to be republished here.
Thank you, Karen.

Koi Carp logo


Aimed primarily at beginners to the hobby, this series of articles will take you step by step through the process of understanding how a good koi pond works.

Update to the nitrate reducing trickle tower design first published in part 16 of this series.

My Trickle Tower Build by
Simon Morris

Simon’s story:
I have been struggling with my nitrate levels which were in excess of 75 mg/L and supporting a very healthy growth of blanket weed - so when I saw Syd’s trickle tower design I decided to give it a go.

I contacted Syd by email several times and he always came back with in-depth answers that made the whole process very simple.

As a result my trickle tower is now in position.



Pond, 5,500 gallons, Nexus 300 + Bakki Shower with 80 kg BHM



A few of the pond residents



Plastic barrel base with outlet & media support pipe. Barrel was chosen specifically as the outer channel will help collect debris which can then be siphoned out without removing tower etc



Plastic barrel base with outlet pipe & media support pipe, notched to allow water to flow through



Internal view showing stainless steel support bolts and notches cut out to allow water into barrel base



The Dalek invasion is almost complete! Tower showing spray bar and slide valve. Pipe is 30cm diameter, 100cm tall, will hold approx 70ltr of Hel X media



Media support tray (base of a plastic garden riddle)



Media support tray in position, located on stainless steel bolts and supported in the middle by section of 4” pipe



Outlet and pipe work with tower in position



Other end of spray bar with rubber end stop



Top of tower (plastic plant pot tray) which will be siliconed to rim around top of drain pipe once Hel X media in position



Return pipe to shower from skimmer with insulation (scaffold pipe protection)



Tower in position!



Water return to pond



View of spray bar, no media yet!



Outlet & pipe work



It works! But still no media!


Part 16 published my variation on an old design for an anaerobic nitrate reducing trickle tower. It was sufficiently detailed to allow an averagely competent koi keeper to build one for themselves.

For these towers to work efficiently, or in fact to even work at all, it is vital that a few principles are understood and incorporated.  My design addressed the common reasons why trickle towers sometimes fail to deliver the required results and included small modifications to make tower design far more efficient.

Following publication of the article, both Koi Carp and I received good feedback and I answered several questions related to clarifying how to build one. Below are answers some of the questions I was subsequently asked and they may provide additional information for anyone planning to build one for themselves. Also included, there are also step-by-step pictorial details of a well built tower based on this design by Simon Morris.

Do you think that ceramic media such as Crystal Bio or Bakki House Media might be more likely to harbour anaerobic bacteria than Bac Bio Balls?
In an aerobic environment, Bac Bio Balls couldn't support the anaerobic respiration mode of these facultative bugs because they would find it far easier to obtain their oxygen directly from the water rather than having to go to the trouble of obtaining it from nitrate.  Denitrifying media has been manufactured so that normal aerobic nitrogen cycle bugs can live on the outside surfaces but the various types of media are all full of almost microscopic cracks and "caves".  Only bugs that can use facultative respiration can live deep inside it. Part 17 in the series explained this in greater detail.

In an anaerobic environment, such as in a trickle tower, any media will be ok because it is the oxygen free environment that forces the facultative bugs to switch to having to obtain their oxygen from nitrate rather than the fact that they are living in an anaerobic environment inside the trickle tower.

In short, any media, including denitrifying media, will do in a trickle tower but expensive denitrifying media will be wasted because its special characteristics won't be needed and won't provide any advantage over ordinary media.

What is the maximum flow rate? I have an 11,000 gallon pond so I need to remove nitrate from a lot of water.
Flow rates are more dependent on feeding regimes than actual pond volumes but a larger pond implies many koi and, as a result, a high feed rate so the amount of nitrate that will be produced by your conventional filter potentially will be quite high.

Trickle towers are literally towers with just a trickle of water going through them so the amount of water flow is only small.  Once they have matured, they will remove all trace of nitrate from that trickle but the flow rate of a small trickle tower may not keep up with the rate at which nitrate is being manufactured by the size of your conventional filters.  The best advice in your situation with such a large pond would be to build a large trickle tower, ideally at least 2 metres tall and at least 30 cm in diameter. They cannot be too big as long as you can lift them off of the tray at the bottom of my design in order to clear any silt that may begin to build up.

The greater volume of media inside larger trickle towers will allow a greater flow or, if it would be practical, you could have several smaller ones. They won't need individual pumps, just a single feed that is capable of supplying each with an adjustable trickle.  You should be able to obtain that from your existing pump(s).

Is it possible for anaerobic bacteria to contaminate the pond and should water return to the pond via a UV sterilizer?
The bugs no-one wants in their ponds are nasty ones called heterotrophic bacteria. These include pseudomonas aeruginosa which like to live in deep anaerobic silt deposits feeding on rotting organic matter but they will infect any fish that roots around in that silt.  These types of bug are not the ones that take up residence in a trickle tower unless you allow it to silt up which is why my design has a tray at the bottom where any build-up can be seen and removed before it becomes a suitable home for such bacteria.

There are far too many species of bacteria that can set up home in a trickle tower to state which ones are the most likely but one bacteria that is on the short list is one called Bacillus Subtilis. These bugs are common soil bacteria with possibly one million of them living in a single gram of ordinary soil.  Wind action will soon ensure that specks of dust from soil will carry either the bugs themselves or their spores (sort of “bug eggs”) into the pond.  It is benign and B. Subtilis has an interesting range of uses in a pond.  It is even an “ingredient” in some probiotic Koi foods so if B. Subtilis set up home in a trickle tower there will be no danger that it will escape and infect the fish.

You said that the type of media is almost irrelevant but as my tower will be one metre high and 30cm in diameter I want to make sure that it is going to work to is maximum capacity.  I have a choice of the following:  Crystal Bio, Oase Hel X media or a mixture of Kaldness K1 & K3 media. Which would you recommend for the best performance?
Any of those will work perfectly well in a trickle tower so if you have one of them already available that won’t be used for the biological stages of another filter then don’t waste it, use that one.  If you are intending to buy new media, then the properties of Crystal Bio will be wasted in a trickle tower.  It's already a denitrifying media that doesn't need to be kept in an oxygen free environment in order to support facultative anaerobic respiration.

Hel X and Kaldness will not support facultative anaerobic bacteria in an environment where there is oxygen freely available, or at least it won’t support them in their anaerobic respiration (nitrate reducing) mode. In a trickle tower, either type will be able to support facultative bugs in that mode of respiration because there is no oxygen inside it so either of these would be suitable.

Of the two types, Hel X and Kaldness, the data for the Hel X media says that it has the greatest surface area, meaning that it will have more room for bugs to set up home so, given a free choice, that would be the one I'd use.

I know you said to start off with the slowest flow possible to allow the bugs to establish and to test the nitrate level to establish if flow could be increased once less than 5 mg/l had been reached, but what sort of flow rate do you think I ought to be starting with?
Working out a value for flow rates for these kinds of filters isn't practical since much will depend on the species of bacteria that will set up home in them but, as a guide, they cannot be too slow for denitrification to take place so you can literally start with a dribble.  Due to the lack of oxygen in the tower, bacterial reproduction rates will be very slow so you may not see very much happen for a couple of weeks.

Measure the nitrate in the output water. At first it will be the same as the input water but, as the facultative anaerobe bugs begin to multiply, the nitrate level will become lower. When there is a significant reduction (5 mg/L is a guide) you can increase the flow by a very small amount. If the nitrate level increases, wait for a few days until it falls again.  Keep doing this until you get the maximum flow with the minimum nitrate level in the output.  This will be the most effective rate of nitrate reduction you will be able to get from that size trickle tower.

Should I clean the media in some potassium permanganate to strip off the waxy coating as I have seen on a couple of forums, if so, for how long should it soak and at what dosage?
When manufacturing these types of media, lubricants are used to make the surfaces slippery and reduce friction during the moulding or plastic extrusion processes. When the media is used for biological filtration, bacteria will be unable to settle onto the surface until all traces of these lubricants either wear or are washed away. Removing them with potassium permanganate will speed up the maturation of plastic media whichever bugs we are trying to encourage.

Potassium permanganate removes oils by a process called oxidation. It is active as long as the solution remains purple and it goes brown as it becomes "used up".  This is exactly the same as happens when it is used as a pond treatment but, whereas pond use requires a strictly controlled dose rate and top up doses in order not to harm the fish, no such restrictions apply when it is just being used to clean or sterilise media.

Air stones are essential in order to keep the dissolved oxygen level from dropping when using potassium permanganate as a medication but they can also be used when cleaning media. Not for the effect on dissolved oxygen but because they will keep the solution well mixed without having to keep stirring it by hand.

The amount of potassium permanganate necessary for effective cleaning is 1.5 gm per 1,000 litres (6.8 gm per 1,000 imperial gallons.  Since the amount necessary for the much smaller volume of water you will need for soaking the media will be too small to measure, I would suggest that you put the media in a container with enough water to cover it and simply stir in sufficient potassium permanganate to turn the water a deep shade of purple. Adding an air stone isn't strictly necessary but it will keep the solution continuously mixed and circulating. If the water begins to turn brown, simply add extra small amounts of potassium permanganate as necessary to ensure it stays purple for at least four hours.

After that, just rinse the media well to remove all traces of the treatment and it can be used straight away.

Would it help to ‘seed’ the top of the media in the tower with K1 out of my Nexus?
The best answer I can give to that question is that it probably will help but certainly wouldn't hinder. The biofilm that exists on matured conventional media doesn't only contain ammonia bugs and nitrite bugs; it contains many others as well.  The top few centimetres of the media in a trickle tower, as described in part 16, becomes colonised by ammonia and nitrite bugs which perform the normal nitrogen cycle process.  This uses all available oxygen in the incoming water which causes anaerobic conditions to exist deeper down in the media and this provides the perfect environment for facultative bugs.  In this respect, adding mature media will help a little although, in a mature pond, there will be some free floating nitrifying bugs that will soon be carried into the trickle tower anyway.

That initial phase of the maturation process will be quicker if the tower is seeded with mature media but won't take much longer if it isn't. The second phase of maturation, growing a colony of facultative bugs in the anaerobic environment deeper in the media, will always be a slow process.  This is because, where oxygen isn't present, bacterial development only happens in slow motion. It will be pure chance whether or not the biofilm on the mature media will already also contain facultative bugs that will be able to switch to obtaining their oxygen from nitrate in the oxygen free environment deep in the media. If it does contain some these bugs, then adding the mature K1 will help speed up the second phase, if it doesn't, then it won't.  Either way, the maturation can only be speeded up, not slowed down.

Should the spray bar have slots cut into it with a hacksaw blade or could I drill 5mm holes?
My design showed a slotted pipe because I thought that might be the easiest way to distribute water evenly over the top surface of the media with the low flow rate that a trickle tower needs for it to work properly but if you prefer holes in the pipe instead there's no reason why this wouldn't be equally effective.

All situations will be different so there is room to experiment to see what suit your situation best.  In my design, the top distribution pipe hasn't been permanently glued into the top of the tower, it is held in place and sealed with silicone mastic.  Similarly, the end cap has also been push-fitted and held in place with a self tapping screw, possibly with a smear of silicone if necessary to prevent it leaking a few drips. This is deliberate in order that the end cap can be removed so that the slots or holes in the spray pipe can be cleaned if they ever become blocked. The elbow that feeds the incoming water into the pipe could equally be left unglued and could be push-fitted and held with a self tapping screw in the same manner as the end cap.  If this is done, the spray pipe could easily be removed and redrilled or have extra slots cut if you feel this would improve the distribution. If nothing is glued, the pipe could even be entirely replaced with a new pipe with a different arrangement of slots or holes until the distribution is ideal. There is plenty of scope for anyone who enjoys tinkering!

I'd suggest that 5 mm holes might be too large so it might be best if you start with small holes, maybe 3 mm, then try it and increase the diameters of the holes or drill more as you see fit.   In the design, the top cap is also removable so that occasional inspection is possible during normal operation.  This will allow you to remove it to check the results of any alterations you make.  But bear in mind that removing it will allow air into the tower, which will interrupt its good work.  Also, the media can't mature properly if the cap is removed too frequently.  This means that it will be best to get all the tinkering done as soon as is possible then replace the top cap and leave it alone apart from the occasional inspection.

As we are approaching the end of the season and my water temp is only just at 20°C is it worth starting the trickle tower now or should I wait until next season?
I don't see any reason why you shouldn't start now.  The current temperatures are high enough to begin the maturation process.  Bacterial activity will slow down as temperatures fall but low temperatures are unlikely to completely halt the process until winter sets in.  Even then, the bacteria won't completely die as long as you continue to keep water flowing through the tower.

I assume from your question that you won't be heating the pond during winter, but I expect that you will, at least, be covering it.  If so, I'd suggest that you also wrap the tower with a few of layers of bubble wrap and insulate any exposed pipe work so that neither the tower nor the pipe work can freeze.  If you do this, any bacterial colonies that have begun to develop will survive the winter in a dormant state and that will give the tower a head start when temperatures begin to rise again next spring.

There are too many species of bugs that potentially could colonise the media to be specific but, in general, bacterial colonies don't completely die in winter.  During their normal active temperature range there will be new bugs being "born" all the time and there will be other bugs that will die of the bug equivalent of old age. For a colony to remain stable or to grow in size, the rate at which new bugs are "born" must equal or exceed the rate at which older bugs die.

As temperatures drop below the active range of any particular species, the bugs will stop multiplying so there will be no new ones to replace those that die.  The rate at which the older ones die is likely to slow right down but there will still be some deaths. With no new bugs to replace them, it is true that the colony size will slowly reduce during cold spells but, with millions or billions of bugs in a colony, it will take a very long time for cold temperatures alone to completely wipe them out.  The surviving bugs will "wake up" as soon as temperatures rise and they will begin multiplying again so that the "birth" rate will soon outstrip the death rate and the colony will soon reach the full size that its supply of nutrients will allow.

In short, start your trickle tower now.  With an unheated pond, winter will probably set it back a little but it will soon recover next spring.